Tablet-making machines typically include relatively movable upper and lower punches for compressing a charge of material into a tablet. The machines usually include a die head having a plurality of die cavities and axially-extending passageways in which the punches are mounted for reciprocation. Typically, the punches are driven by cams which allow for the filling of the material between the punches, compression of the material, and ejection of the formed tablet. However, the means for controlling the reciprocation of the punches, such as the cams, do not always positively control the movement of the punches which results in the formation of tablets having various drawbacks.
For example, when one of the driving cams does not engage the punch, the punch has a tendency to drop downwardly relative to the die head. As a result, excess air is entrapped within the die cavity so that the material to be compressed does not hold together well due to the entrapped air, and the tablet splits. This problem is referred to the art as "capping". In addition, when the punch is being driven to eject the formed tablet, there is also a tendency for the punch to "bounce", "flutter", or "twist" during its movement which may result in the material being impacted more than once, so that it may break the tablet or cause double impressions.
In the prior art, means have been provided for applying pressure between the punches and the die head. Typically, such means include an external restrainer surrounding the die head to engage rods which extend through the die head to apply pressure to the punches. However, the punch pressure inside the die head or socket cannot be precisely adjusted with such an arrangement. Also, because of such lack of adjustment, the punches cannot be adjusted to compensate for wear of the rod tips, sockets, and punches. Another crude method used in the past was to place a spring in a groove around the lower die head. This required special modification of the press, was greasy, and the spring did not maintain constant positive pressure on the punch.
Broadly, it is an object of the present invention to provide an improved punch which overcomes one or more of the aforesaid problems. Specifically, it is within the contemplation of the present invention to provide an improved punch which is constructed to prevent undesired movements of the punches relative to the die head.
It is a further object of the present invention to provide an improved punch which includes means to prevent the punch from dropping upon being disengaged by the machine drive and to also prevent punch "bounce", "flutter", or "twist" during movement of the punches.
It is a still further object of the present invention to provide an improved punch which eliminates the entrapment of excess air during the supplying of material to the die cavity and thereby overcomes the problem of tablet capping.
It is a still further object of the present invention to provide an improved punch in which the punch pressure may be precisely preset and which may be easily adjusted prior to being installed in the die head.
It is a still further object to provide an improved punch which reduces wear on the drive means for the punches and the punch heads due to their positive control and which may be adjusted to compensate for wearing of the machine components.